1. Field of the Invention
The present invention relates to a device of a light-emitting diode, and a method for fabricating the same. More particularly, the present invention relates to a device of a light-emitting diode using a weakened structure for being separated from a substrate, and a method for fabricating the same.
2. Description of Related Art
There are horizontal structures and vertical structures for Light-emitting diodes (LED) in application. For a conventional horizontal LED device, since electrodes are disposed at a same side, there may have a current crowding phenomenon at a mesa portion of the LED device, which can lead to a poor heat dissipation effect, and accordingly limit an amount of a driving current that the LED can sustain. Presently, the vertical structure is generally adopted for a high power LED.
As shown in FIG. 1A, after a LED device 102 and a mirror/adhesive layer 104 are grown on an epitaxial substrate 100, the LED device 102 is transferred to a carrier substrate 108 through the adhesive layer 104 according to a wafer bonding method. Next, as shown in FIG. 1B, the epitaxial substrate 100 is removed. Next, in FIG. 1C, metal electrodes 110 are respectively formed on a surface of the LED device 102 and a surface of the carrier substrate 108, so as to form the vertical structure. As shown in FIG. 1C, due to a configuration the vertical electrodes, the distribution of current I is better. Moreover, since the carrier substrate 108 is generally formed by a material with a good conductivity and a better heat dissipation effect, such as silicon, copper, aluminium, copper/tungsten, etc., an operation efficiency of the LED device can be improved.
However, a present method for separating the epitaxial substrate is a laser lift-off (LLO) method disclosed by the U.S. Pat. No. 6,071,795. A KrF laser is used to irradiate an interface between the substrate and a gallium nitride layer from the side of the epitaxial substrate, so as to be separated from the epitaxial substrate after the interface absorbs sufficient energy. The epitaxial substrate can be directly removed by a grinding method. In addition, a wet etching process is used together with the grinding method, by which the substrate is grinded thinner, and then an etching solution is used to dissolve the remained substrate. However, when using the LLO method, since it is not easy to control the laser energy, the device surface is liable to be damaged. For a fragile substrate, such as a gallium arsenide substrate, the grinding method is not applicable. Though, for a substrate fainted by a relatively hard material, such as sapphire, gallium nitride, aluminium nitride, etc., it may take a rather long time to perform the grinding. Moreover, in case of the method of grinding and then wet etching, the method is only applicable to the gallium arsenide substrate or a silicon substrate, and is not applicable to the gallium nitride substrate, the aluminium nitride substrate, or the sapphire substrate.